Low driving voltage white organic light-emitting diodes with high efficiency and low efficiency roll-off

Abstract

Single emission layer white organic light-emitting diodes (WOLEDs) showing high color stability, low turn-on voltage, high efficiency and low efficiency roll-off by incorporating iridium(III) bis[(4,6-difluo-rophenyl)-pyridinato-N,C2] (FIrpic) and bis(2-phenylbenzothiazolato) (acetylacetonate)iridium(III) (Ir(BT)2(acac)) phosphors dyes have been demonstrated. Our WOLEDs without any out-coupling schemes as well as n-doping strategies show low operating voltages, low turn-on voltage (defined for voltage to obtain a luminance of 1cd/m2) of 2.35V, 79.2cd/m2 at 2.6V, 940.5cd/m2 at 3.0V and 10300cd/m2 at 4.0V, respectively, and achieve a current efficiency of 40.5cd/A, a power efficiency of 42.6lm/W at a practical brightness of 1000cd/m2, and a low efficiency roll-off 14.7% calculated from the maximum efficiency value to that of 5000cd/m2. Such improved properties are attributed to phosphors assisted carriers transport for achieving charge carrier balance in the single light-emitting layer (EML). Meanwhile the host–guest energy transfer and direct exciton formation process are two parallel pathways serve to channel the overall excitons to dopants, greatly reduced the unfavorable energy losses.